Esophageal cyst in the duodenum of a foal.

A 21-day-old Thoroughbred colt was euthanized following a history of recurrent colic. A 4.5 cm in diameter, occlusive, submucosal cyst was identified in the duodenum at necropsy. Histologically, the cyst was surrounded by a smooth muscle wall and was lined by both squamous and attenuated cuboidal to columnar epithelium. A diagnosis of an esophageal cyst was made based on the gross and histologic findings.